End Boom Load??? Which size Mainsheet Blocks??

[swanny]

I am replacing some of my sail handling blocks and chose Harken as recommended by many. My old 62mm Tufnol 'Hye' branded blocks made excellent brakes. Thing is, I don't really know what size to go for. I have now in my posession two Harken 3" triple sheave midrange blocks which look great but are larger than the old Hye's. I used the seemingly excellent online Harken boat calculater to decide upon these and it told me my boom has a 712kg end boom load. The main is a fully battened, laminated, heavy reinforced sail of 23sqmetres which I have to say does challenge the old Hye blocks. The safe working load of the new blocks are 1700kgs but the next level down with Harken have a safe working load of only 680kg. Am I missing something here? I went for the larger because of the newer reistance with the new mainsail but perhaps with a new mainsheet and blocks, albeit smaller than I have ordered, would be perfectly ok. Should the blocks be sized for a potentially hard accidental gybe or just the force required to sheet in the boom on a close reach in heavy weather?

 

[MoodySabre]

I've always though the vulnerable bit was the little shackle that attaches the top block to the boom or the snap-shackle on the bottom. You want blocks that give you the power you need. 3" sheaves certainly sound pretty meaty. Did you use the calculator on this site? http://www.ybw.com/lewmar/blocks.html

 

[swanny]

thanks for that Moodysabre. You might be right but as the shackles that come with the blocks I have and on the lesser blocks I was considering were 8mm, I thought perhaps they wouldn't be the weakest link. In actual fact, the chandlery in Flensburg, Germany gave me the blocks to try before I buy which was very nice eh!. It could be I go for the slightly smaller ones in the end simply on aesthetics as the 3" ones are as you say pretty meaty looking. I looked at the Lewmar site but didn't come away any the wiser. The Harken calculator chews all the specs of your boat and comes up with weights and measurements and of course the specific blocks you need from them. They recommended the 3" blocks but I have to say the price brought tears to my eyes! But I don't want to penny pinch if its right for the boat. Anymore?

 

[William_H]

The safe working load for the blocks should be way above that you will experience. You need large blocks because they have reduced friction losses which means you can pull the main sheet in tighter especially when the wind is in the sail on a reach.
I have sailed a bit ona 40ft fracttional racing baot ie big mainsail. That has tripple blocks ie 6 purchase but this makes a huge effort to pull in a lot of rope even though thye sheet goes to about 2/3 of the way out the boom. This boat has a 4 purchase adjustment on the tail normally fixed part of the sheet for fine tuning. ie 24 purchase for the last bit of tightening.

I can't imagine your mainsail is that big and you might find a 4 purchase main sheet is adequate if you can get it to a winch for tightening or fit another purchase on the tail. The problem with 6 purchase (triple blocks) is that the friction starts to get really significant especially when you want to release the sheet.

So it is a complex subject but certainly go for the bigger blocks if you can afford them. Especially if you were not satisfied with the old ones. olewill

 

[swanny]

Hi William, thanks for your reply. My mainsheet is on the end of the boom. She's an old gal and all lines are at the mast. The mainsail is not that big really, being a masthead ketch. However, I noticed a big difference in the effort to haul it in from the old sail to the new one which took me by surprise. Of course, like I said, it could be I can replace with the same size blocks or even smaller as with new blocks and a new mainsheet, it would have to be an improvement. I am going to try the big blocks this weekend - I am sure they will prove to be almost effortless compared to the old. The main concern I have is the size and when I am off the wind how the bottom block will hang around, banging on the companionway. Harken of course offer a spring system to keep it off the ground but I need their mainsheet car for this and to have this I need their mainsheet track as mine is 36mm X track. A couple of financial steps too far this year with new sails, engine, heater, upholstery, cooker etc etc. I have ordered a Pfeifer Mainsheet car without control blocks as I don't want the clutter of more lines and I can easily move the car by hand when I want it. We shall see. The big blocks cost here €735 for one three sheave and one three sheave with clamp - Gulp! But I will get at least 15% off I think. It would be about two hundred Euros less for the slightly smaller but lower safe working load ones. I will post back how I get on this weekend. I'm off to boil some porridge for dinner - there has to be some sacrifices with boating!!!

 

[grafozz]

look at the "easymatic " range of multiple mainsheet blocks i use the easymatic 2 system on my 38 ft cat , big roach ,powerful main 2 speed sheeting , works a treat !